Feasibility of artificial intelligence-driven interfractional monitoring of organ changes by mega-voltage computed tomography in intensity-modulated radiotherapy of prostate cancer.

PURPOSE: High-dose radiotherapy (RT) for localized prostate cancer requires careful consideration of target position changes and adjacent organs-at-risk (OARs), such as the rectum and bladder. Therefore, daily monitoring of target position and OAR changes is crucial in minimizing interfractional dosimetric uncertainties. For efficient monitoring of the internal condition of patients, we assessed the feasibility of an auto-segmentation of OARs on the daily acquired images, such as megavoltage computed tomography (MVCT), via a commercial artificial intelligence (AI)-based solution in this study. MATERIALS AND METHODS: We collected MVCT images weekly during the entire course of RT for 100 prostate cancer patients treated with the helical TomoTherapy system. Based on the manually contoured body outline, the bladder including prostate area, and rectal balloon regions for the 100 MVCT images, we trained the commercially available fully convolutional (FC)-DenseNet model and tested its auto-contouring performance. RESULTS: Based on the optimally determined hyperparameters, the FC-DenseNet model successfully auto-contoured all regions of interest showing high dice similarity coefficient (DSC) over 0.8 and a small mean surface distance (MSD) within 1.43 mm in reference to the manually contoured data. With this well-trained AI model, we have efficiently monitored the patient's internal condition through six MVCT scans, analyzing DSC, MSD, centroid, and volume differences. CONCLUSION: We have verified the feasibility of utilizing a commercial AI-based model for auto-segmentation with low-quality daily MVCT images. In the future, we will establish a fast and accurate auto-segmentation and internal organ monitoring system for efficiently determining the time for adaptive replanning.

Hepatic steatosis index at diagnosis has the potential for forecasting end-stage kidney disease in patients with antineutrophil cytoplasmic antibody-associated vasculitis.

Objective: This study evaluated whether the hepatic steatosis index (HSI) at antineutrophil cytoplasmic antibody-associated vasculitis (AAV) diagnosis could forecast poor outcomes during the disease course in AAV patients. Methods: This study included 260 AAV patients. The equation for HSI is as follows HSI=8×(alanine aminotransferase/aspartate aminotransferase)+body mass index+(2, diabetes mellitus)+(2, female). The cut-off of HSI was obtained using the receiver operating characteristic curve. Results: The median age of the 260 patients was 59.5 years, and 65.0% were female. Among the continuous variables excluding the parameters composing the equation for HSI, HSI was significantly correlated with Birmingham vasculitis activity score, five-factor score, haemoglobin, blood urea nitrogen, serum creatinine, and total cholesterol. Among poor outcomes, the area under the curve of HSI for end-stage renal disease (ESRD) was significant, and the cut-off of HSI for ESRD was set at ≤30.82. AAV patients with HSI ≤30.82 exhibited a significantly higher risk of ESRD (relative risk 3.489) and a significantly lower cumulative ESRD-free survival rate than those with HSI >30.82. Conclusion: This study is the first to demonstrate that HSI at AAV diagnosis could forecast ESRD during the disease course in AAV patients.

Feasibility of internal-source tracking with C-arm CT/SPECT imaging with limited-angle projection data for online in vivo dose verification in brachytherapy: A Monte Carlo simulation study.

PURPOSE: The current protocol for use of the image-guided adaptive brachytherapy (IGABT) procedure entails transport of a patient between the treatment room and the 3-D tomographic imaging room after implantation of the applicators in the body, which movement can cause position displacement of the applicator. Moreover, it is not possible to track 3-D radioactive source movement inside the body, even though there can be significant inter- and intra-fractional patient-setup changes. In this paper, therefore, we propose an online single-photon emission computed tomography (SPECT) imaging technique with a combined C-arm fluoroscopy X-ray system and attachable parallel-hole collimator for internal radioactive source tracking of every source position in the applicator. METHODS AND MATERIALS: In the present study, using Geant4 Monte Carlo (MC) simulation, the feasibility of high-energy gamma detection with a flat-panel detector for X-ray imaging was assessed. Further, a parallel-hole collimator geometry was designed based on an evaluation of projection image quality for a 192Ir point source, and 3-D limited-angle SPECT-image-based source-tracking performances were evaluated for various source intensities and positions. RESULTS: The detector module attached to the collimator could discriminate the 192Ir point source with about 3.4% detection efficiency when including the total counts in the entire deposited energy region. As the result of collimator optimization, hole size, thickness, and length were determined to be 0.5, 0.2, and 45 mm, respectively. Accordingly, the source intensities and positions also were successfully tracked with the 3-D SPECT imaging system when the C-arm was rotated within 110° in 2 seconds. CONCLUSIONS: We expect that this system can be effectively implemented for online IGABT and in vivo patient dose verification.

Characterization of Base Oil Effects on Aged Asphalt Binders Considering Bicycle Road.

Demand for various bicycles and sharing systems has constantly been growing worldwide as they improve the quality of life and promote eco-friendly transportation. Accordingly, it is inevitable that bicycle roads should be expanded. As bicycle roads have a relatively lower load applied than automobile roads, adopting a design method that uses a high reclaimed asphalt pavement (RAP) content can be beneficial. However, much uncertainty still exists about the relation between the mixing method and application in field sites, without appropriately considering the quality control of the rejuvenator. Therefore, this study aims to demonstrate the effect of base oil as a rejuvenator on aged binders, considering the use of a high RAP content for bicycle roads. To prepare the aged binder, a rolling thin-film oven (RTFO) and pressure aging vessel (PAV) were used to imitate the life cycle of asphalt pavement from production to service life, and then three contents of aged binder (0%, 50%, and 100%) were added and mixed with fresh PG 64-22 base binder. Finally, each type of prepared aged asphalt binder was blended with three different base oil contents (0%, 5%, and 10%). The results indicated that (1) the addition of base oil effectively decreased the viscosity of aged binders, (2) aged binders containing base oil showed less G*/sin δ compared to originally aged binders, and (3) the application of base oil improves the cracking properties of the aged binder by decreasing stiffness. In conclusion, the most striking observation from the data analysis from the Superpave test and statistical results was the effect of reducing the asphaltene portion based on the use of base oil in the aged binder. Therefore, using base oil in RAP can enable the application of a high RAP content to the bicycle road.

An Investigation of Body Size Impact on Organ Doses for Neutron External Exposures Using the MRCP-based Phantom Library.

ABSTRACT: In a recent study, a comprehensive library composed of 212 phantoms with different body sizes was established by deforming the adult male and female mesh-type reference computational phantoms (MRCPs) of ICRP Publication 145 and the next-generation ICRP reference phantoms over the current voxel-type reference phantoms of ICRP Publication 110. In this study, as an application of the MRCP-based phantom library, we investigated dosimetric impacts due to the different body sizes for neutron external exposures. A comprehensive dataset of organ/tissue dose coefficients (DCs) for idealized external neutron beams with four phantoms for each sex representatively selected from the phantom library were produced by performing Monte Carlo simulations using the Geant4 code. The body size-dependent DCs produced in this study were systematically analyzed, observing that the variation of the body weights overall played a more important role in organ/tissue dose calculations than the variation of the body heights. We also observed that the reference body-size DCs based on the MRCPs indeed significantly under- or overestimated the DCs produced using the phantoms, especially for those much heavier (male: 175 cm and 140 kg; female: 165 cm and 140 kg) than the reference body sizes (male: 176 cm and 73 kg; female: 163 cm and 60 kg) by up to 1.6 or 3.3 times, respectively. We believe that the use of the body size-dependent DCs, together with the reference body-size DCs, should be beneficial for more reliable organ/tissue dose estimates of individuals considering their body sizes rather than the most common conventional approach, i.e., the sole use of the reference body size DCs.

Fatty Liver Index Independently Predicts All-Cause Mortality in Patients With Antineutrophil Cytoplasmic Antibody-Associated Vasculitis but No Substantial Liver Disease.

Background: This study investigated whether the fatty liver index (FLI) could predict all-cause mortality and cerebrovascular accident (CVA) during follow-up in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) without substantial liver disease. Methods: The medical records of 75 AAV patients with AAV were retrospectively reviewed. An equation for the FLI is as follows: FLI = (e0.953×loge(triglycerides)+0.139×BMI+0.718×loge(GGT)+0.053×waistcircumference-15.745)/(1 + e0.953×loge(triglycerides)+0.139×BMI+0.718×loge(GGT)+0.053×waistcircumference-15.745) × 100. The cut-offs of the FLI were obtained using the receiver operator characteristic (ROC) curve analysis. Results: The mean age at AAV diagnosis was 59.1 years and 42.7% were male. Eight patients (10.7%) died and 8 patients had CVA during follow-up. When the cut-offs of the FLI for all-cause mortality and CVA were set as the FLI ≥ 33.59 and the FLI ≥ 32.31, AAV patients with the FLI over each cut-off exhibited a higher risk for all-cause mortality or CVA than those without (RR 8.633 and 8.129), respectively. In addition, AAV patients with the FLI over each cut-off exhibited a significantly lower cumulative patients' survival rate or CVA-free survival rate than those without, respectively. In the multivariable Cox analysis, only the FLI ≥ 33.59 at AAV diagnosis was an independent predictor of all-cause mortality during follow-up in AAV patients (HR 10.448). Conclusion: The FLI at AAV diagnosis can be a potential independent predictor of all-cause mortality and CVA during follow-up in AAV patients. We suggest that physicians measure the FLI at AAV diagnosis and pay more attention to those with a high FLI value for prevention of future mortality and CVA.

Long-Term Feasibility of 13.56 MHz Modulated Electro-Hyperthermia-Based Preoperative Thermoradiochemotherapy in Locally Advanced Rectal Cancer.

We evaluated the effect of 13.56 MHz modulated electro-hyperthermia (mEHT) boost in neoadjuvant treatment for cT3-4- or cN-positive rectal cancer. Sixty patients who completed the mEHT feasibility trial (ClinicalTrials.gov Identifier: NCT02546596) were analyzed. Whole pelvis radiotherapy of 40 Gy, mEHT boost twice a week during radiotherapy, and surgical resection 6-8 weeks following radiotherapy were performed. The median age was 59. The median follow-up period was 58 (6-85) months. Total/near total tumor regression was observed in 20 patients (33.3%), including nine cases of complete response. T- and N-downstaging was identified in 40 (66.6%) and 53 (88.3%) patients, respectively. The 5-year overall and disease-free survival were 94.0% and 77.1%, respectively. mEHT energy of ≥3800 kJ potentially increased the overall survival (p = 0.039). The ypN-stage and perineural invasion were possible significant factors in disease-free (p = 0.003 and p = 0.005, respectively) and distant metastasis-free (p = 0.011 and p = 0.034, respectively) survival. Tumor regression, resection margin status, and other molecular genetic factors showed no correlation with survival. Although a limited analysis of a small number of patients, mEHT was feasible considering long-term survival. A relatively low dose irradiation (40 Gy) plus mEHT setting could ensure comparable clinical outcomes with possible mEHT-related prognostic features.

Development of a direction-sensitive gamma-ray monitoring system using a gamma camera with a dual-sided collimator: A Monte Carlo study.

Nuclear explosions, sabotage, and dirty bomb materials are considered a security threat. This paper discusses the development of a gamma-ray monitoring system that enables the screening of nuclear materials moving simultaneously on both sides of the system at ports. This direction-sensitive gamma-ray monitoring (DSGM) system consists of a monolithic plastic scintillator surrounded by 28 photomultiplier tubes and dual-sided parallel-hole lead collimators. With Monte Carlo simulation, the monitoring performance of the DSGM system was assessed for static and moving sources. A multilayer perceptron model was employed to estimate the energy-deposited position of the gamma-rays emitted by nuclear materials in the scintillator.

Development of integrated prompt gamma imaging and positron emission tomography system for in vivo 3-D dose verification: a Monte Carlo study.

An accurate knowledge of in vivo proton dose distribution is key to fully utilizing the potential advantages of proton therapy. Two representative indirect methods for in vivo range verification, namely, prompt gamma (PG) imaging and positron emission tomography (PET), are available. This study proposes a PG-PET system that combines the advantages of these two methods and presents detector geometry and background reduction techniques optimized for the PG-PET system. The characteristics of the secondary radiations emitted by a water phantom by interaction with a 150 MeV proton beam were analysed using Geant4.10.00, and the 2-D PG distributions were obtained and assessed for different detector geometries. In addition, the energy window (EW), depth-of-interaction (DOI), and time-of-flight (TOF) techniques are proposed as the background reduction techniques. To evaluate the performance of the PG-PET system, the 3-D dose distribution in the water phantom caused by two proton beams of energies 80 MeV and 100 MeV was verified using 16 optimal detectors. The thickness of the parallel-hole tungsten collimator of pitch 8 mm and width 7 mm was determined as 200 mm, and that of the GAGG scintillator was determined as 30 mm, by an optimization study. Further, 3-7 MeV and 2-7 MeV were obtained as the optimal EWs when the DOI and both the DOI and TOF techniques were applied for data processing, respectively; the detector performances were improved by about 38% and 167%, respectively, compared with that when applying only the 3-5 MeV EW. In this study, we confirmed that the PG distribution can be obtained by simply combining the 2-D parallel hole collimator and the PET detector module. In the future, we will develop an accurate 3-D dose evaluation technique using deep learning algorithms based on the image sets of dose, PG, and PET distributions for various proton energies.

Radioisotope identification using an energy-weighted algorithm with a proof-of-principle radiation portal monitor based on plastic scintillators.

In this study, we validated the feasibility of an energy weighted algorithm that highlights a characteristic area including the Compton edge as a single peak in a proof-of-principle radiation portal monitor system with a plastic scintillator measuring 50 × 100 × 5 cm3. We measured the energy weighted spectra with steel shielding and the dynamic movements of the 137Cs and 60Co sources. The results showed that the peak locations of each source could be identified under shielded or dynamic motion conditions, each within a maximum difference of 0.08 MeV.

Monte Carlo simulation of a 2D dynamic multileaf collimator to improve the plan quality in radiotherapy plan: a proof-of-concept study.

The leaf width of a multileaf collimator (MLC) determines the dose conformity to the target volume. The objective of this study was to investigate the feasibility of a two-dimensional dynamic MLC (2DDMLC) to improve the treatment plan quality with a fixed leaf width. The treatment head of the Clinac™ linear accelerator with the Millennium 120™ MLC was modelled with the Geant4 (for GEometry ANd Tracking) tollkit using the Monte Carlo (MC) method. The 2DDMLC produces a beam aperture by moving the MLC bank vertically to the leaf movement. Thus, the effect of the 2DDMLC motion on beam divergence and beam fluence resolution was evaluated by comparing the dose distributions between the conventional MLC motion and the 2DDMLC. Finally, the 2DDMLC was employed for dynamic conformal arc therapy for 13 brain cancer patients. The dose-volumetric parameters, including the dose delivered to 98% of the target volume (D 98%), percent volume given 20% of the prescribed dose (V 20%), and conformity index (CI) were compared with those of the conventional MLC. For the 6 MV beam of the MC model, the depth dose and lateral dose distribution differed by less than 2% between the simulation and measurement. The 2DDMLC did not significantly influence beam divergence and sharpened the beam. In clinical use, the dose delivered to the target was almost identical between the 2DDMLC and conventional MLC (D 98% = 29.74 Gy versus 29.71 Gy, p  = 0.18). The CI was improved with the use of the 2DDMLC (CI = 1.49 versus 1.47, p  = 0.14). Moreover, irradiation of normal tissue was reduced with the 2DDMLC compared with conventional MLC (V 20% = 17.22% versus 17.45%, p  < 0.001). The 2DDMLC improved the dose conformity to the target volume and reduced the irradiation of the normal tissue compared with the conventional MLC.

Development of accurate dose evaluation technique of X-ray inspection for quality assurance of semiconductor with Monte Carlo simulation.

Since higher dose delivered to a semiconductor leads to more functional loss to the device, accurate dose evaluation of the semiconductor is very important to reduce the defect rate during x-ray inspection. The aim of this study is to develop the technique to accurately evaluate the absorbed dose to the semiconductor using the Monte Carlo method. The x-ray radiographic system was modeled based on the Geant4 Monte Carlo tool-kit. The Monte Carlo commissioning was performed by comparing the energy spectrum between the simulation and measurement. The dose evaluation technique for the semiconductor was developed, and the dose delivered to the semiconductor device was evaluated according to various x-ray energies. The energy spectrum of the x-ray beam simulated with Geant4 was validated with the experiment using the CdTe detector for various x-ray beams. The accurate dose to the semiconductor component was assessed according to various x-ray energies. The x-rays of 25 keV energy delivered the highest dose to the silicon die, while the 67.5 keV showed the minimum dose to the die. It was observed that the higher energy over about 70 keV also increased the dose with the scattered photons produced in the solder ball and circuit board. The technique to accurately determine the absorbed dose in the semiconductor was suggested and the x-ray energy deliver the high dose to the semiconductor die was assessed. These results could be fundamentally used to reduce the dose in semiconductor and defect rate in x-ray inspection.

Development of advanced skin dose evaluation technique using a tetrahedral-mesh phantom in external beam radiotherapy: a Monte Carlo simulation study.

Incorrect prediction of skin dose in external beam radiotherapy (EBR) can have normal tissue complication such as acute skin desquamation and skin necrosis. The absorbed dose of skin should be evaluated within basal layer, placed between the epidermis and dermis layers. However, current treatment planning systems (TPS) cannot correctly define the skin layer because of the limitation of voxel resolution in computed tomography (CT). Recently, a new tetrahedral-mesh (TM) phantom was developed to evaluate radiation dose realistically. This study aims to develop a technique to evaluate realistic skin dose using the TM phantom in EBR. The TM phantom was modeled with thin skin layers, including the epidermis, basal layer, and dermis from CT images. Using the Geant4 toolkit, the simulation was performed to evaluate the skin dose according to the radiation treatment conditions. The skin dose was evaluated at a surface depth of 50 µm and 2000 µm. The difference in average skin dose between depths was up to 37%, depending on the thickness and region of the skin to be measured. The results indicate that the skin dose has been overestimated when the skin is evaluated using commercial TPS. Although it is not possible with traditional TPS, our skin dose evaluation technique can realistically express the absorbed dose at thin skin layers from a patient-specific phantom.

Determining the energy spectrum of clinical linear accelerator using an optimized photon beam transmission protocol.

PURPOSE: The complex beam delivery techniques for patient treatment using a clinical linear accelerator (linac) may result in variations in the photon spectra, which can lead to dosimetric differences in patients that cannot be accounted for by current treatment planning systems (TPSs). Therefore, precise knowledge of the fluence and energy spectrum (ES) of the therapeutic beam is very important. However, owing to the high energy and flux of the beam, the ES cannot be measured directly, and validation of the spectrum modeled in the TPS is difficult. The aim of this study is to develop an efficient beam transmission measurement procedure for accurately reconstructing the ES of a therapeutic x-ray beam generated by a clinical linac. METHODS: The attenuation of a 6 MV photon beam from an Elekta Synergy Platform clinical linac through different thicknesses of graphite and lead was measured using an ion chamber. The response of the ion chamber as a function of photon energy was obtained using the Monte Carlo (MC) method in the Geant4 simulation code. Using the curves obtained in the photon beam transmission measurements and the ion chamber energy response, the ES was reconstructed using an iterative algorithm based on a mathematical model of the spectrum. To evaluate the accuracy of the spectrum reconstruction method, the reconstructed ES (ESrecon ) was compared to that determined by the MC simulation (ESMC ). RESULTS: The ion chamber model in the Geant4 simulation was well validated by comparing the ion chamber perturbation factors determined by the TRS-398 calibration protocol and EGSnrc; the differences were within 0.57%. The number of transmission measurements was optimized to 10 for efficient spectrum reconstruction according to the rate of increase in the spectrum reconstruction accuracy. The distribution of ESrecon obtained using the measured transmission curves was clearly similar to the reference, ESMC , and the dose distributions in water calculated using ESrecon and ESMC were similar within a 2% local difference. However, in a heterogeneous medium, the dose discrepancy between them was >5% when a complex beam delivery technique composed of 171 control points was used. CONCLUSIONS: The proposed measurement procedure required a total time of approximately 1 h to obtain and analyze 20 transmission measurements. In addition, it was confirmed that the transmission curve of high-Z materials influences the accuracy of spectrum reconstruction more than that of low-Z materials. A well-designed transmission measurement protocol suitable for clinical environments could be an essential tool for better dosimetric accuracy in patient treatment and for periodic verification of the beam quality.

Development of a Geant4-based independent patient dose validation system with an elaborate multileaf collimator simulation model.

Despite the improvements in the dose calculation models of the commercial treatment planning systems (TPS), their ability to accurately predict patient dose is still limited. One of the limitations is caused by the simplified model of the multileaf collimator (MLC). The aim of this study was to develop a Monte Carlo (MC) method-based independent patient dose validation system with an elaborate MLC model for more accurate dose evaluation. Varian Clinac 2300 IX was simulated using Geant4 toolkits, after which MC commissioning with measurements was performed to validate the simulation model. A DICOM-RT interface was developed to obtain the beam delivery conditions including the hundreds of MLC motions. Finally, the TPS dose distributions were compared with the MC dose distributions for water phantom cases and a patient case. Our results show that the TPS overestimated the absolute abutting leakage dose in the closed MLC field, with about 20% more of the maximum dose than that of the MC calculation. For water phantom cases, the dose distributions inside the target region were almost identical with the dose difference of less than 2%, while the dose near the edge of the target shows difference about 10% between Geant4 and TPS due to geometrical differences in MLC model. For the patient analysis, the Geant4 and TPS doses of all organs were matched well within 1.4% of the prescribed dose. However, for organs located in areas with high ratio of leaf pairs with distances less than 10 mm leaf pair (LP(<10mm) ), the maximum dose of TPS was overestimated by about 3% of the prescribed dose. These dose comparison results demonstrate that our system for calculating the patient dose is quite accurate. Furthermore, if the MLC sequences in treatment plan have a large ratio of LP(short) , more than 3% dose difference in normal tissue could be seen.

Development of a PMMA phantom as a practical alternative for quality control of gamma knife® dosimetry.

BACKGROUND: To measure the absorbed dose rate to water and penumbra of a Gamma Knife® (GK) using a polymethyl metacrylate (PMMA) phantom. METHODS: A multi-purpose PMMA phantom was developed to measure the absorbed dose rate to water and the dose distribution of a GK. The phantom consists of a hemispherical outer phantom, one exchangeable cylindrical chamber-hosting inner phantom, and two film-hosting inner phantoms. The radius of the phantom was determined considering the electron density of the PMMA such that it corresponds to 8 g/cm2 water depth, which is the reference depth of the absorbed dose measurement of GK. The absorbed dose rate to water was measured with a PTW TN31010 chamber, and the dose distributions were measured with radiochromic films at the calibration center of a patient positioning system of a GK Perfexion. A spherical water-filled phantom with the same water equivalent depth was constructed as a reference phantom. The dose rate to water and dose distributions at the center of a circular field delimited by a 16-mm collimator were measured with the PMMA phantom at six GK Perfexion sites. RESULTS: The radius of the PMMA phantom was determined to be 6.93 cm, corresponding to equivalent water depth of 8 g/cm2. The absorbed dose rate to water was measured with the PMMA phantom, the spherical water-filled phantom and a commercial solid water phantom. The measured dose rate with the PMMA phantom was 1.2% and 1.8% higher than those measured with the spherical water-filled phantom and the solid water phantom, respectively. These differences can be explained by the scattered photon contribution of PMMA off incoming 60Co gamma-rays to the dose rate. The average full width half maximum and penumbra values measured with the PMMA phantom showed reasonable agreement with two calculated values, one at the center of the PMMA phantom (LGP6.93) and other at the center of a water sphere with a radius of 8 cm (LGP8.0) given by Leksell Gamma Plan using the TMR10 algorithm. CONCLUSIONS: A PMMA phantom constructed in this study to measure the absorbed dose rates to water and dose distributions of a GK represents an acceptable and practical alternative for GK dosimetry considering its cost-effectiveness and ease of handling.

Independent dose validation system for Gamma Knife radiosurgery, using a DICOM-RT interface and Geant4.

Leksell GammaPlan was specifically designed for Gamma Knife (GK) radiosurgery planning, but it has limited accuracy for estimating the dose distribution in inhomogeneous areas, such as the embolization of arteriovenous malformations. We aimed to develop an independent patient dose validation system based on a patient-specific model, constructed using a DICOM-RT interface and the Geant4 toolkit. Leksell Gamma Knife Perfexion was designed in Geant4.10.00 and includes a DICOM-RT interface. Output factors for each collimator in a sector and dose distributions in a spherical water phantom calculated using a Monte Carlo (MC) algorithm were compared with the output factors calculated by the tissue maximum ratio (TMR) 10 algorithm and dose distributions measured using film, respectively. Studies using two types of water phantom and two patient simulation cases were evaluated by comparing the dose distributions calculated by the MC, the TMR and the convolution algorithms. The water phantom studies showed that if the beam size is small and the target is located in heterogeneous media, the dose difference could be up to 11%. In the two patient simulations, the TMR algorithm overestimated the dose by about 4% of the maximum dose if a complex and large bony structure was located on the beam path, whereas the convolution algorithm showed similar results to those of the MC algorithm. This study demonstrated that the in-house system could accurately verify the patient dose based on full MC simulation and so would be useful for patient cases where the dose differences are suspected.

An effective dose assessment technique with NORM added consumer products using skin-point source on computational human phantom.

The aim of this study is to develop the assessment technique of the effective dose by calculating the organ equivalent dose with a Monte Carlo (MC) simulation and a computational human phantom for the naturally occurring radioactive material (NORM) added consumer products. In this study, we suggests the method determining the MC source term based on the skin-point source enabling the convenient and conservative modeling of the various type of the products. To validate the skin-point source method, the organ equivalent doses were compared with that by the product modeling source of the realistic shape for the pillow, waist supporter, sleeping mattress etc. Our results show that according to the source location, the organ equivalent doses were observed as the similar tendency for both source determining methods, however, it was observed that the annual effective dose with the skin-point source was conservative than that with the modeling source with the maximum 3.3 times higher dose. With the assumption of the gamma energy of 1MeV and product activity of 1Bqg-1, the annual effective doses of the pillow, waist supporter and sleeping mattress with skin-point source was 3.09E-16SvBq-1year-1, 1.45E-15SvBq-1year-1, and 2,82E-16SvBq-1year-1, respectively, while the product modeling source showed 9.22E-17SvBq-1year-1, 9.29E-16SvBq-1year-1, and 8.83E-17SvBq-1year-1, respectively. In conclusion, it was demonstrated in this study that the skin-point source method could be employed to efficiently evaluate the annual effective dose due to the usage of the NORM added consumer products.

Effective dose evaluation of NORM-added consumer products using Monte Carlo simulations and the ICRP computational human phantoms.

The aim of this study is to evaluate the potential hazard of naturally occurring radioactive material (NORM) added consumer products. Using the Monte Carlo method, the radioactive products were simulated with ICRP reference phantom and the organ doses were calculated with the usage scenario. Finally, the annual effective doses were evaluated as lower than the public dose limit of 1mSv y(-1) for 44 products. It was demonstrated that NORM-added consumer products could be quantitatively assessed for the safety regulation.